Microactuator

ABSTRACT

The present invention relates to a microactuator that can be produced by utilizing the IC fabrication processes such as etching, lithography or the like and that can be used as a micropositioner in a multi probe head for scanning probe microscopy and a pickup head for recording and reproducing equipment. 
     The microactuator comprises a plurality of electrodes arranged around the circumference of a circle, a ring-like displacement plate located inside said electrodes, beams which support said displacement plate elastically at one ends and at the same time are fixed at the other ends to a point located towards the inside of said displacement plate on a substrate and a voltage supply means to apply voltages to said electrodes in order for said electrodes to attract said displacement plate electrostatically. 
     An extremely small, long life and high reliability microactuator that is excellent in mass-producibility and capable of high precision positioning can be realized.

This application is a divisional of application Ser. No. 08/082,956filed Jun. 29 1993 now U.S. Pat. No. 6,472,794.

BACKGROUND OF THE INVENTION

The present invention relates to a microactuator that can be fabricatedaccording to the IC fabrication processes characterized by etching andlithography, for example, and can be used as a micropositioner for themultiple probe head of a scanning probe microscope and the pickup headfor a signal recording and reproduction equipment.

As a first prior art example of a microactuator, there is anelectrostatic micro wobble motor introduced in a paper authored byMehregany et al. (“Operation of microfabricated harmonic and ordinaryside-drive motors”, proceedings of the third IEEE Workshop on MicroElectro Mechanical Systems, Napa Valley, Calif. USA, Feb. 11-14, 1990,pp. 1-8)

FIG. 50 is a schematic plan view to show how this prior artelectrostatic micro wobble motor is structured and FIG. 51 is across-sectional view of the foregoing motor.

In FIG. 50 and FIG. 51, item 1 is a bearing, item 2 is a rotor of about100 μm in diameter and items 3 a through 3 h are eight electrodesarranged around the periphery of the rotor 2. (On a photograph of themotor in the above referenced paper, there are 12 static polesobserved.) Although not shown in the drawings, these electrodes areconnected by wires with a voltage supply source and can be applied withvoltages arbitrarily selected.

As indicated in FIG. 50, the rotor 2 is shaped like a ring and betweenthe inner circumference thereof and the bearing ⁻ 1 there exists aclearance C. Therefore, in contrast to an ordinary motor, the rotor 2does not rotate around the bearing 1 with the bearing serving as theaxis of rotation. As voltages are applied to electrodes 3 a through 3 hin succession, the rotor 2 revolves since it is attracted sequentiallytowards the excited electrodes 3 a through 3 h.

At the same time, however, since the rotor 2 moves while it is inrolling contact with the bearing 1 at the contact point of 2 a, therotor 2 rotates by the difference between the outer circumference of thebearing 1 and the inner circumference of the rotor 2. A detaileddescription on this performance will be made later.

The rotor 2 is held by a flange 1 a so that it does not slip off fromthe bearing 1. The electrodes 3 a through 3 h (only 3 a and 3 e areshown in FIG. 51) are almost of the same height as the rotor 2. On thebottom surface of the rotor 2, there are a plurality dot-like sounds 2b, not a ring-like mound, which slide on and contact electrically with ashield layer 4.

FIG. 52 through FIG. 56 are the cross-sectional illustrations to showthe fabrication processes (a) through (e), respectively, for theelectrostatic micro wobble motor, which will be described hereunder. Thefabrication processes employ the ordinary IC fabrication methods such asetching, lithography or the like.

(a) As illustrated in FIG. 52, an insulating layer 6 is first formed ona silicon substrate 5 by depositing in succession an oxide layer of 1 μmin thickness grown thermally and a silicon nitride layer of 1 μm inthickness formed by means of a low pressure chemical vapor depositionmethod (LPCVD).

Then, a polysilicon thin film of 3500 Å thick with phosphorus diffusedsufficiently therein is formed by LPCVD and patterning is appliedthereto to complete an electric shield layer 4.

Further, a low temperature oxide layer (LTO) 7 of 2.2 μm thick isdeposited to make a first sacrificial layer and then patterning isapplied by 2 steps, the one for forming a base 7 a of the electrodes 3 athrough 3 h and the other for forming a hollow 7 b in preparation ofcreating a mound 2 b on the bottom of the rotor 2.

(b) As illustrated in FIG. 53, a polysilicon layer of 2.5 μm thickdiffused with phosphorus sufficiently is deposited by LPCVD and then therotor 2 and the electrodes 3 a through 3 h (only 3 a and 3 e are shownhere) as indicated in FIG. 50 and FIG. 51 were formed by means of areactive ion etching method (RIE). As shown in FIG. 53, the electrodes 3a through 3 h are fixed on the silicon substrate 6 and a plurality ofthe mound 2 b are formed on the bottom of the rotor 2. On account of athermal oxidation layer after patterning used as the mask for thereactive ion etching of the foregoing polysilicon layer, the thicknessof the rotor 2 as well as the electrodes 3 a through 3 h isapproximately 2.2 μm at this stage.

(c) As illustrated in FIG. 54, an LTO layer 8 to make a secondsacrificial layer of about 0.3 μm thick is deposited for retaining theclearance C between the bearing 1 and the rotor 2. At the same time, ananchor 8 a for the bearing 1 is formed by patterning.

Although the diameter of the bearing 1 is about 36 μm, the smallestpossible diameter is 26 μm due to the restrictions imposed by theprocess employed here.

(d) As illustrated in FIG. 55, a polysilicon layer of 1 μm thick withphosphorus diffused sufficiently is deposited by LPCVD and the bearing 1provided with the flange 1 a is formed.

(e) As illustrated in FIG. 56, the LTO layers 7 and 8 serving as thefirst and second sacrificial layers respectively are dissolved bybuffered hydrogen fluoride (HF) and the rotor is released completely torealize the structure as shown in FIG. 51.

The operational principle of the prior art electrostatic micro wobblemotor having a structure as described above will be explained in thefollowing with the help of FIG. 50. As stated before, the rotor 2 doesnot rotate around the bearing 1 with the bearing serving as the axis ofrotation. Instead, the rotor revolves as it is attracted by the excitedelectrodes 3 a through 3 h sequentially and at the same time it rotatesby the difference between the outer circumference of the bearing 1 andthe inner circumference of the rotor 2 while it is in rolling contactwith the bearing 1 at the contact point 2 a.

In other words, suppose the electrodes are excited in the direction X asindicated in FIG. 50 in an order of the electrodes 3 a, 3 b, 3 c and soforth, then the rotor 2 is first attracted by the excited electrode 3 a.Next, it will be attracted by the electrode 3 b and then by theelectrode 3 c and so forth, resulting in revolving of the rotor 2 alsoin the direction X.

Since the clearance C between the rotor 2 and the bearing 1 is set up tobe smaller than the gap between the rotor 2 and the electrodes 3 athrough 3 h, there will be the contact point 2 a where the rotor 2 willcome into contact with the bearing 1. Besides, the correct gap betweenthe rotor 2 and the electrodes 3 a through 3 h corresponds to G+E asindicated in FIG. 50, where the E means an effective gap length thatproduces the motor's torque, and the following relationship isestablished inherently from the structure of the motor:

E=G−C>0

(This is obvious when the state of the electrode 3 e being excited hasbeen observed.) As the gap between the rotor 2 and the electrodes 3 athrough 3 h, G will be dealt with for convenience because of thepossibilities in reducing the effective gap length E to the minimum.

Now, as the rotor 2 revolves in the direction X, the contact point 2 aalso is to move likewise in the direction X. Since the bearing 1 isfixed in position, slipping at the contact point 2 a by the amount ofthe difference between the outer circumference of the bearing 1 and theinner circumference of the rotor 2 is taking place unless the rotor 2revolves. However, attracting force is applied to the rotor 2 in thedirection of pressing the bearing 1 and practically any slipping hardlyoccurs at the contact point 2 a.

Therefore, as the rotor 2 revolves in the same direction as the shiftingdirection (the direction of X) of the voltages applied to the electrodes3 a through 3 h, the rotor 2 is consequently to rotate in the samedirection (the X direction of FIG. 50) by the amount corresponding tothe difference between the outer circumference of the bearing 1 and theinner circumference of the rotor 2. It is needless to say that thecontact point 2 a is to move in the direction X while it is in the stateof rolling contact.

The feature of this electrostatic micro wobble motor is in that therevolution frequency of the revolving rotor 2 is determined by the outerdiameter B of the bearing 1 and the inner diameter R of the rotor 2, andthe revolution frequency S of the revolving rotor 2 is to becomeextremely small against the shifting frequency F of the input voltages(the physically shifting frequency of the voltages applied to theelectrodes 3 a through 3 h for the present prior art example) whencompared with the case of an ordinary motor.

In case wherein the revolution frequency of the revolving motor 2 isequal to the shifting frequency F of the input voltages, the revolutionfrequency S of the revolving rotor 2 is expressed by the followingequation:

S=F×(R−B)/R=F×C/R

Since the revolution speed is reduced to S/F, e.g. C/R, the torque willbe increased, instead, to R/C times in contrast to the case of anordinary motor. In addition, by reducing the clearance C, the slippageat the contact point 2 a can be eliminated, resulting in advantageouslysuppressing the wobbling of the rotor 2 caused by its revolution.

An a result, a motor of low speed and high torque has been realizedwithout using any speed reduction means in particular and greatlyexpected to be used as the motive force or the like for micromachines.

On the other hand, the scanning probe microscopes, typically representedby STM (Scanning Tunneling Microscope), have been prevailing widely andrapidly in recent years as a means to observe minute objects on thesurface of specimens for the high resolution and the feature that themicroscopes can be used under any measurement environments in principle.Especially, the progress in development of the STM has been remarkableand many research studies have been made on the methods to produceprobing needles and cantilevers by fine fabrication processing ofsilicon. These efforts have been aiming at down-sizing of the equipmentby micro-miniaturizing the mechanical parts involved and alsoimprovement of the vibration resistant characteristics by increasing theresonant frequencies of the mechanical parts.

These probing needles and cantilevers are generally referred to asprobes and usually driven finely by piezo elements separately prepared.Therefore, the dimensions of the whole mechanical parts are mostlyaccounted for by the dimensions of piezo elements even when the probesare reduced in size.

Studies have been recently started to create a thin film piezo elementon a cantilever for micro-deforming the cantilever itself and some studyresults have already been made public.

As a second prior art example of a microactuator, there is a thin filmprobe which has been used as a probe head for scanning probe microscopesand was introduced by a paper authored by Akamine et al. (“A planarprocess for Micro-fabrication of a Scanning Tunneling Microscope”,Sensors & Actuators, A21-23, pp. 964-970, 1990)

FIG. 57 shows how the aforementioned prior art thin film probe isstructured.

In FIG. 57, item 101 is a silicon substrate and item 102 is acantilever, on the end point of which a probing needle 103 is beingattached. The cantilever 102 measures 8 in thickness by 200 in width by1000 μm in length.

The cantilever 102 is fundamentally of a bimorph structure consisting ofthin film piezo elements 104 and 105. On the upper surface of the thinfilm piezo element 104 are formed electrodes 106 a through 106 c and onthe bottom surface of the thin film piezo element 105 are formedelectrodes 107 a and 107 b, which are almost identical in configurationwith the electrodes 106 a and 106 b, respectively. Besides, an electrode108 is formed between the thin film piezo elements 104 and 105 and alsothe probing needle 103 is fixed on the electrode 106 c.

As illustrated in FIG. 57, electrical wirings are provided to connecteach of the electrodes 106 a through 106 c, 107 a, 107 b and 108respectively with pads, through which arbitrary voltages can be appliedto the electrodes.

FIG. 58 through FIG. 62 are cross-sectional illustrations of thefabrication processes (a) through (b) for the above thin film probe,wherein the generally known semiconductor processes such as etching,lithography or the like are utilized. With the help of the foregoingillustrations, the fabrication processes will be explained brieflyhereunder.

(a) As shown in FIG. 58, a membrane 109 of 50 to 70 μm thick is formedthrough an application of anisotropic etching to the bottom surface ofthe silicon substrate 101.

(b) As shown in FIG. 59, electrodes 107 a and 107 b (not shown in FIG.59) are formed by deposition of a first Al thin layer to a thickness of0.5 μm by means of electron beam evaporation and then by patterningthereof.

(c) As shown in FIG. 60, a thin film piezo element 105 is formed bysuccessive deposition of a first nitride layer of 0.2 um thick by meansof plasma-enhanced chemical vapor deposition (PECVD), a first zinc oxidelayer of 3 μm thick by reactive sputtering and then a second nitridelayer of 0.2 μm thick on the electrodes 107 a and 107 b.

Patterning is performed with the nitride layer by means of plasmaetching and with the zinc oxide layer by wet etching, respectively.

(d) As shown in FIG. 61, a thin film piezo element 104 is formed bysuccessive deposition of a second Al thin layer serving as electrode 108according to the same steps as (b), and a third nitride layer, a secondzinc oxide layer and a fourth nitride layer by means of PECVD andreactive sputtering according to the same steps as (c) on the foregoingthin film piezo element 105. Further, electrodes 106 a through 106 c(only 106 a is shown in FIG. 61) are formed by deposition of a third Allayer according to the same steps as (b) on the thin film piezo element105.

(e) As shown in FIG. 62, the membrane 109 is lastly removed from thebottom surface of the substrate by plasma etching to complete thestructure as indicated in FIG. 57.

Next, how this thin film probe operates will be explained briefly withthe help of FIG. 63 through FIG. 66.

As is generally known, a piezo element has a property of expansion orcontraction depending on the direction of the electric field appliedthereto. Therefore, by applying an appropriate voltage of eitherpositive or negative polarity to the electrodes 106 a, 106 b, 107 a and107 b while the electrode 108 is kept grounded, the cantilever 102 canbe freely deformed through a control of the electric field that isapplied to the thin film piezo elements 104 and 105.

As illustrated in FIG. 63 for example, when voltages of the samepolarity are applied to the electrodes 106 a, 106 b, 107 a and 107 b andalso electric fields of the same direction are applied to the thin filmpiezo elements 104 and 105, the cantilever 102 as a whole will showexpansion or contraction in the longitudinal direction. (X direction inFIG. 63).

Also, as illustrated in FIG. 64 through FIG. 66 by hatched lines(indicating that closely spaced diagonal lines rising towards right meanthe applied voltage to be positive, for example, and loosely spacedlines rising towards left mean the applied voltage to be negative), whenthe electric fields applied to the thin film piezo elements 104 and 105are controlled by applying a positive or a negative voltage to eachrespective electrode, it will be possible to provide the end of thecantilever 102 with such motions of high freedom as moving in thehorizontal direction (the Y direction in FIG. 64) or in the verticaldirection (the Z direction in FIG. 65) or twisting as indicated by anarrow M in FIG. 66.

Accordingly, the probing needle 103 attached to the end of thecantilever can be precisely moved for the purpose of scanning a specimensince the piezo elements have extremely high resolution.

Thus, a thin film probe for the scanning probe microscopy can be made bydepositing piezo elements on a silicon substrate through semiconductorfabrication processes and it is expected that the employment of thisprobe will greatly contribute to the production of an extremely smalland high performance scanning probe microscope.

Also, magnetic heads for VTR and magnetic disc equipment and opticalheads for optical disc equipment are generally known as the conventionalpickup heads for recording and reproducing equipment. Efforts have beenalways made to make the recording and reproducing equipment smaller insize and larger in recording capacity. For that purpose, development andprogress of the precision mechanism technology as typically applied tohigh density recording and pickup heads is absolutely necessary.

There is a probe recording method among many new approaches proposed atpresent for the high density recording. This method is to use a probingneedle as used with a STM or the like as a head for mechanical scanning.

The probing needle type charge storage recording, for example, asdescribed in a paper authored by Barrett et al. (“Charge storage in anitride-oxide-silicon medium by scanning capacitance microscopy”, J.Appl. Phys. Vol. 70, No. 5, pp. 2725-2733, Sep. 1, 1991) proves thepossibility of high density and non-destructive recording andreproducing.

The principle of operation thereof will be explained here briefly. Whenan electro-conductive probing needle mounted on a cantilever of an AFM(Atomic Force Microscope) is kept in contact with a dielectrics layer(silicon nitride), which is placed on an electro-conductive body, andapplied with a bias voltage, electric charges will be trapped by thedielectrics layer and information will be stored therein. Reproductionof the information is performed by detecting capacitance existentbetween the probing needle and the substrate by means of a sensor. It ispossible to erase the information by applying a reversed bias voltageand also perform recording repeatedly.

The recording medium is prepared by depositing an oxide layer and anitride layer on a polysilicon substrate which was added with boron. Byhaving a probing tip of tungsten placed in contact with the aboverecording medium and a voltage of −25 V applied for 20 μsec.,information of 75 nm bits have been recorded. The recording density hasreached as many as 180 bits/μm², more than 200 times the conventionalrecording.

The first prior art structure as exemplified in the foregoing tends tohave torque loss due to rolling friction since the dot-like mounds onthe rotor bottom are in contact with the shield layer and also theflange is in contact with the rotor while the rotor is revolving.Besides, various parts of the motor suffer from mechanical wears due tofriction over a long period, resulting in a considerable reduction inthe life of the motor.

Further, the rotor and the shield layer tend to fail in having therespective potentials kept at the same level in a stable manner sincethe electrical contact between them is performed through a slidingaction between the dot-like mounds under the rotor bottom and the shieldlayer surface, resulting in deteriorated reliability.

Furthermore, since the rotational characteristics of the motor aregoverned by the dimensional accuracy of the outer diameter of thebearing, the outer and inner diameters of the rotor, and the innerdiameter of the electrode lay-out, it is difficult to gain stablerotational accuracy.

In addition, the difficulty in taking out the torque of the rotor forpossible utilization in a micropositioner on account of the rotor movingonly in the inner space inside the boundary formed by the electrodelay-out has presented a problem.

Also, It is required according to the second prior art structure asexemplified in the foregoing to move either the entire thin film probeincluding the silicon substrate 101 or the specimen in order to performa measurement of a different place of the specimen.

Besides, there has been a problem of not being able to observe aparticular surface of a specimen multi-purposely by not only an STM butalso, for example, an AFM or a MFM (Magnetic Force Microscope).

The conventional precision mechanism technology has been mostly involvedwith component parts in the areas of how to put them together, realizinghigher accuracy of them, making them smaller in dimension, laying themout effectively as a whole and so forth. The problem has been in thateven when an innovative progress was made in the recording principle orin the recording medium such innovation was not utilized to the fullestextent in achieving the ultimate miniaturization and performance of therecording and reproducing equipment.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a microactuator thatcan be produced by semiconductor processes, which excel inmicro-miniaturization and mass-producibility, is capable of highaccuracy positioning and also in possession of long life and highreliability.

The structure disclosed by the present invention comprises:

a plurality of electrodes arranged along a circumference on a substrate;

a ring-like displacement plate located inside said electrodes;

beams, each of which is fixed at one end to an anchor solidly formed onsaid substrate and at the other end to a specified place of the innercircumference of said displacement plate in support of said displacementplate elastically; and

a voltage application means whereby voltages are selectively applied tosaid respective electrodes to have said displacement plate attractedelectrostatically towards said electrodes, which have been applied withsaid voltages, and moved.

The foregoing structure as disclosed by the present invention has madeit possible to bring about the following effects:

Since the displacement plate to be driven electrostatically is securelyin electrical contact through the beams, reliability in the drivingcharacteristics of the displacement plate has been greatly enhanced.

The adverse effect due to friction at the time when the displacementplate comes into contact with the electrodes has been made extremelysmall, resulting in longer life.

It has been made possible to control the position and angle of thedisplacement plate very accurately with resultant realization of anexcellent positioning mechanism.

High torque has been obtainable.

It has become possible to design a microactuator for the most suitableconfiguration with abundant freedom.

With the use of semiconductor processes, it has become possible toachieve micro-miniaturization and secure mass-producibility.

Besides, by employing the microactuator of the present invention in amulti-head probe for a scanning probe microscope, a plurality of movablethin film probes can be simultaneously manipulated to realize equipmentwhereby a surface of a specimen is observed in a diversified mannerwithout moving the specimen.

Furthermore, by utilizing the microactuator of the present invention ina pickup head of recording and reproducing equipment, it has becomepossible to provide a microactuator produced by an entirely newfabrication method based on a concept that has not been existent before.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view to show the structure of a microactuatoras a first exemplary embodiment (Example 1) of the present invention.

FIG. 2 is a cross-sectional illustration to show the structure of themicroactuator of Example 1.

FIG. 3 through FIG. 7 are cross-sectional illustrations to show thefabrication processes of the microactuator of Example 1.

FIG. 8 and FIG. 9 are schematic plan views to explain the operation ofthe microactuator of Example 1.

FIG. 10 is a schematic plan view to show the structure of amicroactuator as a second exemplary embodiment (Example 2) of thepresent invention.

FIG. 11 is a plan view to show a plurality of the microactuator as shownin FIG. 10 laid out in a matrix formation on a single substrate.

FIG. 12 is a schematic plan view to show the structure of amicroactuator as a third exemplary embodiment (Example 3) of the presentinvention.

FIG. 13 and FIG. 14 are cross-sectional illustrations to show thestructure of the microactuator of Example 3.

FIG. 15 through FIG. 29 are cross-sectional illustrations to show thefabrication processes of the microactuator of Example 3.

FIG. 30 through FIG. 33 are illustrations to explain the operation ofthe microactuator of Example 3.

FIG. 34 is a schematic plan view to show the structure of amicroactuator as a fourth exemplary embodiment (Example 4) of thepresent invention.

FIG. 35 and FIG. 36 are schematic plan views to explain the operation ofthe microactuator of Example 4.

FIG. 37 is a schematic plan view to show the structure of a multi-probehead for a scanning probe microscope as a fifth exemplary embodiment(Example 5) of the present invention's microactuator.

FIG. 38 is an enlarged view to explain the operation of themicroactuator of Example 5.

FIG. 39 is a schematic plan view to show the component elements of theprobe of the microactuator of Example 5.

FIG. 40 is a longitudinal sectional view along the broken line of POQand looked in the direction of an arrow T as shown in FIG. 39.

FIG. 41 is a traverse sectional view along the broken line RS as shownin FIG. 39.

FIG. 42 through FIG. 44 are schematic plan views to explain theoperation of the probe head of Example 5 for a scanning probemicroscope.

FIG. 45 is a perspective view of the recording and reproducing equipmentthat comprises pickup heads as a sixth exemplary embodiment (Example 6)of the present invention's microactuator.

FIG. 46 is a cross-sectional illustration of the recording andreproducing equipment that consists of pickup heads of Example 6.

FIG. 47 is a plan view to show how the pickup heads of Example 6 are putin position.

FIG. 48 is a partially enlarged plan view to show a positionalrelationship between the pickup head of Example 6 and the disc.

FIG. 49 is a cross-sectional view of the pickup head of Example 6.

FIG. 50 is a schematic plan view to show the structure of anelectrostatic micro wobble motor as a first prior art example.

FIG. 51 is a cross-sectional illustration to show the structure of theelectrostatic micro wobble motor of the first prior art example.

FIG. 52 through FIG. 56 are cross-sectional illustrations to explain thefabrication processes for the electrostatic micro wobble motor of thefirst prior art example.

FIG. 57 is an illustration to show the structure of a thin film probe asa second prior art example.

FIGS. 58 through 62 are cross-sectional illustrations to explain thefabrication processes for the thin film probe of the second prior artexample.

FIG. 63 through FIG. 66 are illustrations to explain the operation ofthe thin film probe of the second prior art example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Details of the present invention will be described by referring toexemplary embodiments hereunder.

EXAMPLE 1

FIG. 1 is a schematic plan view to show the structure of a microactuatoras a first exemplary embodiment of the present invention and FIG. 2 is across-sectional illustration of said microactuator.

In FIG. 1 and FIG. 2, item 10 is an anchor, items 11 a through 11 c arespiral shaped beams, item 12 is a ring-like displacement plate and items13 a through 13 p are 16 electrodes arranged along the circumference ofthe displacement plate 12. These respective electrodes 13 a through 13 pcan be applied in the same way as was in the prior art examples witharbitrary voltages through connecting wires from a voltage supply means.

As indicated by hatched lines in FIG. 1, the displacement plate 12 is aring-like plate measuring approximately 100 μm in outer diameter and 75μm in inner diameter and being supported by the anchor 10, which isabout 15 um in outer diameter and located concentrically with theelectrodes 13 a through 13 p, by means of the three beams 11 a through11 c of an identical configuration attached to the inner circumferenceof the displacement plate 12 at three different positions thereofseparated from each other by 120 degrees. These beams 11 a through 11 care spiral shaped, each measuring several um in width, and locatedsymmetrically from each other with respect to the center of theelectrodes 13 a through 13 p that are laid out along a circumference.

The inner diameter of the circumference laid out by the electrodes 13 athrough 13 p (only the electrodes 13 a and 13 i are shown in FIG. 2) ismade larger than the outer diameter of the displacement plate 12 byseveral um. Also, the electrodes are situated at lower positions thanthe displacement plate and so, when the electrodes are excited, thedisplacement plate 12 will be attracted downwards for its stabilizedmotion.

Besides, the displacement plate 12 is constructed so as to be keptelectrically in contact with a shield layer 14 by means of the beams 11a through 11 c and the anchor 10. In addition, an insulating layer 15 isformed on each respective inner edge of the electrodes 13 a through 13 pin order to prevent the electrodes from making a direct electricalcontact with the displacement plate 12.

FIG. 3 through FIG. 7 are schematic cross-sectional illustrations toexplain the fabrication processes (a) through (b) of this microactuatorrespectively, wherein the general IC fabrication methods such asetching, lithography or the like are utilized. The fabrication processeswill be explained by referring to the respective illustrationshereunder.

(a) As shown in FIG. 3, an insulating layer 17 is formed on a siliconsubstrate 16 by depositing in succession an oxide layer of 1 μm inthickness grown thermally and a silicon nitride layer of 1 μm inthickness formed by means of LPCVD.

Then, a polysilicon thin film of 3500 Å thick with phosphorus diffusedsufficiently therein is formed by LPCVD and patterning is appliedthereto to complete an electric shield layer 14.

(b) As shown in FIG. 4, a low temperature oxide layer (LTO) 18 of 2.2 umthick is deposited to make a sacrificial layer and then patterning isapplied for forming a fixed portion 18 a of the electrodes 13 a through13 p and a hollow 18 b in preparation of creating the anchor 10 for thedisplacement plate 12.

(c) As shown in FIG. 5, a polysilicon layer of 2.5 μm thick diffusedwith phosphorus sufficiently is deposited by LPCVD and then thedisplacement plate 12, the electrodes 13 a through 13 p (only theelectrodes 13 a and 13 i are shown in FIG. 5), the beams 11 a through 11c and the anchor 10 as illustrated in FIG. 1 and FIG. 2 are formed bymeans of a reactive ion etching method (RIE). At this time, theelectrodes 13 a through 13 p and the anchor 10 are fixed on the siliconsubstrate 16.

On account of a thermal oxidation layer after patterning used as themask for the reactive ion etching of the foregoing polysilicon layer,the thickness of the displacement plate 12 as well as the beams 11 athrough 11 c and the electrodes 13 a through 13 p is approximately 2.2μm at this stage.

Besides, the inner diameter of the circumference laid out by theelectrodes 13 a through 13 p is made larger by the thickness of theinsulating layer 15 which will be formed at a later step of thefrabrication processes.

(d) As shown in FIG. 6, a deposit of a thermal oxidation layer to athickness of 0.1 μm and another deposit thereupon of a silicon nitrideto a thickness of 0.34 μm are formed and then patterning is appliedthereto to create an insulating layer 15 on the inner circumference ofeach respective electrode of 13 a through 13 p. At this stage of thefabrication processes, a clearance is left between the outer diameter ofthe displacement plate 12 and each of the electrodes 13 a through 13 p.

(e) As shown in FIG. 7, the LTO layer 18 serving as the sacrificiallayer is lastly dissolved by buffered hydrogen fluoride (HF) and thedisplacement plate 12 and the beams 11 a through 11 c are released torealize the structure as illustrated in FIG. 2.

Next, the operation of the microactuator produced according to theforegoing exemplary embodiment of the present invention will beexplained by the help of FIG. 8 and FIG. 9.

As illustrated in FIG. 8, when the electrode 13 a is excited, thedisplacement plate 12 will be electrostatically attracted and come intocontact with the insulating layer 15 on the inner circumference of theelectrode 13 a.

Then, as illustrated in FIG. 9, as voltages are applied sequentially tothe electrodes 13 a through 13 p, the displacement plate 12 will revolvein the direction of arrow X, being attracted by the excited electrodes13 a through 13 p in sccession.

However, since the displacement plate 12 and the electrodes 13 a through13 p move at that time while both are in rolling contact with each otherat the common contact point, the displacement plate 12 will rotate bythe difference between the inner circumference laid out by theelectrodes 13 a through 13 p and the outer diameter of the displacementplate 12. The rotation of the displacement plate 12 is in the directionof arrow Y, which is opposite to the direction of its revolution.

At this time, although the displacement plate 12 is fixed in position tothe substrate 16 by means of the beams 11 a through 11 c and the anchor10, the displacement plate 12 can be rotated by a specified anglethrough the elastic deformation of the beams 11 a through 11 c, whichare formed in configuration to extend over some length by having themmade narrow in width and spiral in shape.

Conversely, upon removing the excitation from the electrodes 13 athrough 13 p even while the displacement plate 12 is in motion, it willbe possible to have the displacement plate 12 returned readily to theinitial position on account of the rebounding force of the elasticallydeformed beams 11 a through 11 c.

What the present exemplary embodiment differs from the first prior artexample is in the fact that the displacement plate 12 revolving androtating on account of the attracting force caused by the excitedelectrodes 13 a through 13 p is linked to and also supported elasticallyby the anchor 10 by means of a plurality of the spiral beams 11 athrough 11 c and additionally the displacement plate 12 is arranged tocontact on its outer circumference with the electrodes 13 a through 13 pthrough the insulating layer 15.

Therefore, the contact between the rotating displacement plate 12 andthe electrodes 13 a through 13 p is limited to the rolling contact onlyand the adverse effect caused by friction is made extremely small,resulting in a reduction of the deterioration in motionalcharacteristics caused by wear and realization of a long lifemicroactuator.

Besides, the electrostatically driven replacement plate 12 is puttogether with the shield layer 14 through the beams 11 a through 11 cand the anchor 10 and the electrical contact between the two is securelyestablished, enabling to enhance the reliability in the motionalcharacteristics.

Further, since the rotational accuracy of the displacement plate 12 isdetermined only by the roundness of the inner circumference laid out bythe electrodes 13 a through 13 p and the outer circumference of thedisplacement plate 12, control of the accuracy in the fabricationprocesses can be easier when compared with that of the prior artexample. Also, since the displacement plate 12 can be readily returnedto its initial position by the rebounding force of the beams 11 athrough 11 c upon removing the excitation off the electrodes 13 athrough 13 p, the position and angle of the displacement 12 can becontrolled accurately and with good reproducibility, resulting in a goodpossibility of using it as an actuator for positioning.

Furthermore, the microactuator of the present exemplary embodiment makesit possible to utilize the feature of high torque which a wobble motorhas possessed inherently.

This is because the frequency of rotation Q of the displacement plate 12becomes smaller by far than the rotational frequency F of the inputvoltages (the physical rotational frequency of the voltages applied tothe electrodes 13 a through 13 p for the present exemplary embodiment)when compared with that of the ordinary motor in the same way as wasalready observed with the prior art example since the rotationalfrequency of the displacement plate 12 is determined by the innerdiameter A of the circumference laid out by the electrodes 13 a through13 p and also by the outer diameter D of the displacement plate 12.

In case where the frequency of revolution of the displacement plate 12is the same as the rotational frequency F of input voltages, thefrequency of revolution Q of the displacement plate 12 can be expressedby:

Q=F×(A−D)/D

Suppose the difference between the inner diameter of the circumferencelaid out by the electrodes 13 a through 13 p and the outer diameter ofthe displacement plate (about 100 um) is 2 um, for example, therotational frequency of the displacement plate becomes as small as aboutone fiftieth of that of the input voltage. However, since the generatedtorque is inversely proportional to the ratio of the rotationalfrequencies, torque of as high as 50 times the torque from an ordinaryelectrostatically driven motor turning around a fixed axis can begenerated.

Thus, according to the present exemplary embodiment, it is possible toobtain a longer life and higher reliability microactuator compared withthe first prior art example, having little adverse effect of frictionand realizing secure electrical contact at time of electrostatic motion.

In addition, since the control of accuracy in fabricating thedisplacement plate is simplified and the displacement plate can bereturned to the initial state by the rebounding force of theelectrically deformed beams, a positioning mechanism having highaccuracy and excellent reproducibility can be realized.

Besides, it is needless to say that torque as high as that from a wobblemotor can be obtained.

Moreover, since each respective component part is laid out on a plane,the motional characteristics can not be governed by the thickness of thesacrificial layer, there is a possibility of performing the mostsuitable designing with abundant freedom and also the semiconductorprocesses can be utilized for easy fabrication, it will become possibleto provide a microactuator characterized by small dimensions and lightweight and also mass-producibility.

By having the microactuator of the foregoing utilized in building amagnetic head, for example, according to a fine processing on thedisplacement plate, an integrated type head, whereby both the finepositioning and azimuth adjustment are facilitated, can be realized.Also, when it is applied to constuction of a semiconductor laser, ahologram element or the like, its wider applications that are worthusing as various pickups and optical devices can be created.

In the present invention's exemplary embodiment as above, it is possibleto employ a construction wherein an insulating layer is formed on theouter circumference of the displacement plate 12 instead of the innercircumference of each of the electrodes 13 a through 13 p, achieving thesame effect.

As explained in the foregoing, the structure of the first exemplaryembodiment of the present invention comprises:

a plurality of electrodes arranged on a substrate along a circumference;

a ring-like displacement plate located inside said electrodes;

beams located inside the inner circumference of said displacement plate,each of which is connected at one end with an anchor formed solidly onsaid substrate and at the other end with a specified place of the innercircumference of said displacement plate to support said displacementplate elastically; and

a voltage application means for applying voltages selectively to each ofsaid electrodes in order to have said displacement plate attractedelectrostatically towards said electrodes, to which said voltages havebeen applied, and moved.

The present invention has the effects as stated in the following:

According to the present invention, by having voltages appliedselectively to a plurality of electrodes arranged in a circular form ona substrate, a ring shaped displacement plate situated inside saidelectrodes will be revolved and also rotated by electrostatic attractingforce.

At this time, the displacement plate is elastically supported by beamswhich are fixed at the fixing ends thereof to said substrate.

The displacement plate shows enhanced reliability in its motionalcharacteristics on account of the secure electrical contacting achievedwith the electrostatically driven displacement plate through the beams.

Besides, on account of the rotating displacement plate being in rollingcontact with the electrodes, the effect of friction has become extremelysmall and it has been made possible to realize a long lifemicroactuator.

Further, since the rotational accuracy of the displacement plate isdetermined only by the roundness of the electrodes and the displacementplate, accuracy controlling in the fabrication processes can be madeeasier when compared with that in the prior art example.

Still further, since the displacement plate is supported by the beamsand moved while these beams are being deformed elastically, thedisplacement plate will be readily returned to its initial position uponremoval of the excitation from the electrodes by the rebounding force ofthe beams and able to start to rotate again from there.

Therefore, it has become possible to control the position and angle ofthe displacement plate with high accuracy and excellent reproducibility,leading to realization of an excellent positioning mechanism.

Further, the feature of high torque which a wobble motor has inherentlycan be naturally utilized.

In addition, since all the component elements are laid out on a planeand the actuator's performance is not affected by the thickness of asacrificial layer, it has become possible to conduct a designing workwith abundant freedom for achieving the most suitable diameters ofrespective parts, numbers of electrodes and shapes of beams.

Also, on account of the semiconductor processes utilized readily forfabrication, it has become possible to provide a microactuator havingsmall dimensions, light weight and mass-producibility.

EXAMPLE 2

The structure of a microactuator as a second exemplary embodiment of thepresent invention is explained briefly with the help of drawings.

FIG. 10 is a schematic plan view of said microactuator. What differsfrom the first exemplary embodiment of the present invention is inhaving a microactuator together with a drive control circuit, a signalprocessing circuit and a signal detector formed all on one substrate.

The structure and the fabrication method of the area of FIG. 10, whichis surrounded by a one dotted broken line to show the microactuator 21comprising a ring-like displacement plate and electrodes arranged on acircular layout are the same as described in the foregoing firstexemplary embodiment and the explanation thereof will not be given here.The signal detector 22 uses photodiodes, for example, to convert theoptical signals received directly from outside to electrical signals.

A signal processor 23 consists of the signal processing circuit and thedrive control circuit. Electrical signals from the signal detector 22are processed in the signal processing circuit for controlling themagnitude and timing of the voltages to be applied to the actuator 21through the drive control circuit, whereby the displacement plate 12 iscontrolled in turning on and off, speed of rotation, direction ofrotation, rotational angle or the like.

The signal processor 23 is connected electrically with an outside supplysource (not shown in FIG. 10) and the energy to drive the displacementplate into motion is fed from this outside supply source through thesignal processor 23. The signal detector 22 and the signal processor 23are formed in an about 300 μm square area of the substrate as shown inFIG. 10 according to the same semiconductor process as employed infabrication of the actuator 21.

As indicated in FIG. 11, a plurality of the actuators can be puttogether in a matrix formation on one substrate. A system including 64actuators, for example, can be realized by an arrangement of 8 by 8matrix on a substrate of about 2.5 mm square.

Thus, by having the signal detector 22 and signal processor 23integrated with the actuator 21 for its intelligent performance, it hasbecome possible to obtain a very compact microactuator of excellentresponse characteristics. Also, by having a plurality of the actuatorsput in position and driven into controlled motion separately, it, ispossible to realize a microactuator which can be operated either in adistributed or concerted mode.

In this example, photo diodes are used in the signal detector 22 inconverting the optical signals into electrical signals. However,providing the signals from outside get to the signal detector directly,the signals cannot necessarily be optical signals.

With this systematized microactuator, it is possible to expand itsapplications to an optical computer, various types of recording ordisplay equipment and the like because, as mentioned before, variousdevices formed on the displacement plate make it possible to accept orrelease information while the processing of data is performed within thesystem to realize an integrated type device of extremely highcapability.

As explained in the foregoing, the structure of the second exemplaryembodiment of the present invention includes a unit comprising:

a plurality of electrodes arranged on a substrate along a circumference;

a ring-like displacement plate located inside said electrodes;

beams located inside the inner circumference of said displacement plate,each of which is connected at one end with an anchor formed solidly onsaid substrate and at the other end with a specified place of the innercircumference of said displacement plate to support said displacementplate elastically;

a drive control circuit for controlling voltages to be applied to saidelectrodes;

a signal detector for converting signals from outside to electricalsignals; and

a signal processing circuit for processing said electrical signals andtransmitting control signals to said drive control circuit, all beingput together,

and also a plurality of the above unit formed on a single substrate.

The present invention has the effects as stated in the following:

According to the present invention, signals from outside are convertedinto electrical signals in a signal detector and then the electricalsignals are processed in a signal processing circuit into controlsignals which are outputted to a drive control circuit for controllingthe motion of a ring-like displacement plate, which is located inside ofelectrodes arranged in a circular lay-out, through controlling thevoltages applied to the electrodes in the same way as was in the firstexemplary embodiment of the present invention.

The present invention further covers a microactuator produced by layingout a plurality of the foregoing system treated as unit on one substratein a matrix formation. Therefore, by having the signal detector andsignal processor integrated with the actuator for its intelligentperformance, it has become possible to obtain a very compactmicroactuator of excellent response characteristics and at the sametime, by having a plurality of the actuators driven into controlledmotion separately, it is possible to realize a microactuator which canbe operated either in a distributed or concerted mode.

EXAMPLE 3

A third exemplary embodiment of the present invention is explained here.Since there are many similarities in construction between the presentexample and the first exemplary embodiment, a more detailed descriptiongiven to this example will be resulting in a little excessive redundancyin explanation.

FIG. 12 is a schematic plan view to show the structure of amicroactuator as an exemplary embodiment of the present invention.

FIG. 13 is a longitudinal sectional view of said microactuator along thebroken line of POQRS as shown in FIG. 12.

FIG. 14 is a traverse sectional view of said microactuator along thebroken line of TU as shown in FIG. 12.

As illustrated in those drawings, a displacement plate 40 is formed ofan electroconducting thin plate-like material consisting of a ringmember 41 and an arm member 42. As described later in detail, thedisplacement plate 40 is as a whole driven electrostatically intorotational motion by the ring member 41 and also the arm member 42thereof is piezoelectrically driven by a bimorph.

First, the structure of the ring member 41 and the vicinity thereof willbe explained. There are three narrow beams 43 a through 43 c of anidentical spiral configuration attached to the inner circumference ofthe ring member 41 at three different positions thereof separated fromeach other by 120 degrees and located symmetrically from each other. Oneend of these beams is fixed to an anchor 45 which is mounted on asubstrate 44 and standing thereupon. In other words, the displacementplate 40 is supported by the anchor 45 elastically by means of the beams43 a through 43 c.

On an area of the substrate 44 extending beyond the outer circumferenceof the ring member 41, nine electrodes 46 a through 46 i (only theelectrode 46 e is shown in FIG. 13) are laid out along a circumferencewith a small gap left between them and the ring member 41. The innercircumference of each respective electrode except for the electrode 46 ais of one identical arc configuration. However, each respectiveelectrode is not located at an equal spacing from each other. Lines OBthrough OH express reference lines, with respect to which the twoneighboring electrodes are symmetric and the spacing pitch angles ∠AOB,∠BOC, ∠COD, ∠DOE, ∠EOF, ∠FOG and ∠GOH are not the same.

Also, the electrodes 46 a through 46 i are connected by wiring with avoltage supply means, although not indicated in FIG. 12, in the same wayas was in the prior art example so that arbitrarily selected voltagescan be applied to the electrodes.

The displacement plate 40 has a concave position restricting member 56at the place opposite to the electrode 46 a. The electrode 46 a,instead, has a convex guide member 57 which comes together with theposition restricting member 56 and directs the motion of thedisplacement plate 40.

Besides, there is an insulating layer 54 formed on the innercircumference of each of the electrodes 46 a through 46 i to prevent theelectrodes from making direct electrical contact with the ring member41. Also, there is an electroconducting shield layer 51 of the sameshape as the ring member 41 placed between the anchor 45 and thesubstrate 44 so as to maintain an electrical connection with the ringmember 41 at all times.

Next, the structure around the arm member 42 will be explained. The tipof the arm member 42 is located outside of the circumference laid out bythe electrodes 46 a through 46 i. As illustrated in FIG. 12 and FIG. 14,the arm member 42 is sandwiched between piezoelectric layers 47 and 48almost over its entire length. In addition, electrodes 49 a through 49 care formed on the piezoelectric layer 47 and electrodes 50 a and 50 b ofalmost the same shape as the electrodes 49 a and 49 b are formed on thepiezoelectric layer 48. Further, a cone shaped metal electrode 66 iscreated on the electrode 49 c.

Furthermore, an electrode 52 is formed on the substrate 44 opposite tothe arm member 42. An insulating layer 55 is formed on the electrode 52so that the electrode 52 does not come into a direct electrical contactwith the arm member 42. Also, there is a cavity 53 formed at the areaopposite to the electrode 50 a and 50 b.

Besides, the electrodes 49 a through 49 c, the electrodes 50 a and 50 b,the electrode 52 and the electrode 66 can be applied with arbitrarilyselected voltages through connecting wires from a voltage applicationmeans although not shown in the drawings.

FIGS. 15 through 29 are cross-sectional illustrations to explain thefabrication processes (a) through (o) of said microactuator. Thefabrication processes use the general semiconductor processes such asetching, lithography or the like. The fabrication processes will beexplained briefly according to the fabrication process illustrationshereunder.

(a) As shown in FIG. 15, an insulating layer 60 is formed on a siliconsubstrate 44 by depositing in succession an oxide silicon layer of 1 μmthick grown thermally and a silicon nitride layer of 1 μm thick formedby means of plasma CVD.

(b) As shown in FIG. 16, an LPCVD polysilicon thin film of 0.35 μm thickwith phosphorus diffused sufficiently therein in formed on saidinsulating layer 60 and patterning is applied thereto to complete anelectrode 52.

(c) As shown in FIG. 17, an insulating layer 55 is formed on theelectrode 52 by deposition of a silicon oxide layer of 0.1 μm thick andalso depositing a silicon nitride layer of 0.34 μm thick by plasma CVDand then by application of patterning thereto.

(d) As shown in FIG. 18, a silicon oxide layer 62 of 2.2 μm thick toserve as a sacrificial layer is deposited.

(e) As shown in FIG. 19, Al is deposited by electron beam deposition toa thickness of 0.5 μm and then patterning is applied to createelectrodes 50 a and 50 b for driving an arm member 42.

(f) As shown in FIG. 20, a nitride layer of 0.2 μm thick by plasma CVD,a zinc oxide layer of 3 μm thick by reactive sputtering and anothernitride layer of 0.2 μm by plasma CVD are deposited alternatingly overthe foregoing electrodes to form a piezoelectric layer 48.

Patterning is applied to the nitirde layers by plasma etching and to thezinc oxide layer by wet etching, respectively.

(g) As shown in FIG. 21, patterning for an electrode fixing member 63and an anchor fixing member 64 is applied to the silicon oxide layer 62serving as a sacrificial layer.

(h) As shown in FIG. 22, an LPCVD polysilicon layer 65 of 2.5 μm thickdiffused with phosphorus sufficiently is then deposited.

(i) Then, as shown in FIG. 23, a nitride layer of 0.2 μm, a zinc oxideof 3 um and a nitride layer of 0.2 μm are again deposited alternatinglyby either plasma CVD or reactive sputtering to form a piezoelectriclayer 47. Also, patterning is applied by plasma etching or wet etchingin the same way as before.

(j) As shown in FIG. 24, an Al layer of 0.5 μm thick is formed andpatterning is applied thereto to create electrodes 49 a and 49 b (notshown in FIG. 24) for driving the arm member 42 and also an electrode 49c (not shown in FIG. 24) for mounting an electrode 66.

(k) As shown in FIG. 25, a cone-shaped electrode 66 is created on thetip of the electrode 49 c by means of a lift off method.

(l) As shown in FIG. 26, a displacement plate 40, beams 43 a through 43c, an anchor 45 and electrodes 46 a through 46 i (only the electrode 46e is shown in FIG. 26) that were indicated in FIG. 12 and FIG. 13 areformed by reactive ion etching (RIE). At this time, the anchor 45 andthe electrodes 46 a through 46 i are fixed on the silicon substrate 44.Since a thermal oxidation layer after patterning is used as the mask forreactive ion etching of said polysilicon layer the thickness of thedisplacement plate 40, the beams 43 a through 43 c and the electrodes 46a through 46 i measures about 2.2 μm at this time. The innercircumference laid out by the electrodes 46 a through 46 i is madelarger by the length of an insulating layer 54 to be formed at a laterstage of the fabrication processes.

(m) As shown in FIG. 27, a high temperature oxidation layer of 0.1 m anda silicon nitride layer of 0.3 m are deposited successively and thenpatterning by RIE is applied thereto so as to have the insulating layer54 formed on the inner circumference of each of the electrodes 46 athrough 46 i. At this stage of the fabrication processes, a clearance iscreated between the outer diameter of a ring member 41 of thedisplacement plate 40 and the electrodes 46 a through 46 i.

(n) As shown in FIG. 28, the silicon oxide layer 62 serving as thesacrificial layer is dissolved by buffered hydrogen fluoride (HF) andthe displacement plate 40 and the beams 43 a through 43 c are releasedoff the substrate 44. At this time, the piezoelectric layers 47 and 48and also the vicinity of the insulating layer 54 are covered by aprotective coating and dissolving thereof by the buffered hydrogenfluoride is prevented from occurring in advance, although any detailedexplanation thereof is omitted here.

(o) As shown in FIG. 29, a cavity 53 is lastly formed on the siliconsubstrate 44 in the place situated directly under the arm member 42 byetching to complete the structure as illustrated in FIG. 13, althoughany detailed explanation is not given here.

Next, the operation of the microactuator produced according to theforegoing exemplary embodiment of the present invention will beexplained by the help of FIG. 30 through FIG. 33.

When the electrodes 46 a and 46 b are excited by application of voltagesof the same magnitude, the ring member 41 of the displacement plate 40will be attracted electrostatically by said electrodes and moved in thedirection of OA as indicated in FIG. 30 until it comes into contact withthe insulating layer 54. At this time, the position restricting member56 of the displacement plate 40 hits and comes into contact with theguide member 57 of the electrode 46 a and also the periphery of the ringmember 41 will come into close contact with the electrodes 46 a and 46b. As a result, the displacement plate 40 will be led to a specifiedposition for assured initialization in terms of its position. At thesame time, the electrode 66 mounted at the tip of the are member 42 willbe guided to a position 67 a as indicated in FIG. 30.

Next, when the excitation of the electrode 46 a is removed and voltagesare applied to the electrodes 46 b and 46 c, the ring member 41 will beattracted electrostatically by the two electrodes newly excited as shownin FIG. 31 and moved by rotating to a position which is symmetric withrespect to the line OB. Then, the electrode 66 mounted on the tip of thearm member 42 will be guided to a position 67 b as indicated in FIG. 31.

As the pair of electrodes to be excited is shifted by one electrodelength alternatingly, the ring member 41 will be revolving in thedirection of an arrow X by being attracted by the excited two electrodessuccessively. When voltages are lastly applied to the electrodes 46 hand 46 i, the ring member 41 will be moved to the position which issymmetric with respect to the line OH. Then, the electrode 66 mounted onthe tip of the arm member 42 will be guided to a position 67 h asindicated in FIG. 32.

Besides, as the ring member 41 is moved while it is in rolling contactwith the electrodes 46 a through 46 i, it will be rotating by thedifference in length between its outer circumference and the innercircumference laid out by the electrodes 46 a through 46 i. Thedirection of its rotation will be in the opposite direction of itsrevolution as indicated by an arrow Y in FIG. 32.

On account of the same arc configuration that each respectivecircumference of the electrodes 46 b through 46 i assumes, the ringmember 41 will be attracted electrostatically to the center of twoneighboring electrodes upon application of voltages to said twoelectrodes. Therefore, by shifting the electrode pairs to be excited byone electrode alternatingly, it will be possible to give a step-likerotating motion to the ring member 41. Further, by having the rotationalangle of the ring member 41 varied most suitably through alteration ofspacing pitch angles between two neighboring electrodes it will bepossible to have the tip of the arm member 42 shifted at an equal pitch.Accordingly, it will be possible to realize a high accuracy and highlydependable positioning mechanism whereby the electrode 66 of the tip ofthe arm member 42 can be guided at an equal pitch from the position 67 ato the position 67 h as illustrated in FIG. 32.

Although the ring member 41 is fixed the anchor 45 through the beams 43a through 43 c, it can be rotated by a specified angle due to elasticdeformation of the beams 43 a through 43 c. As shown in the drawings, byhaving the beams 43 a through 43 c designed to have narrow width forsmaller stiffness and length of some magnitude through employing aspiral shape, it will become possible to realize the aforementionedelastic deformation with the beams 43 a through 43 c.

Also, when a voltage is applied to the electrode 52 on the substrate 44after the ring member 41 has been rotated by a specified angle, the armmember 42 will be attracted electrostatically towards the substrate 44and drawn by said electrode 52. Then, even if the excitation on theelectrodes 46 a through 46 i is removed, the position of the arm member42 will be kept for assuring a precise positioning.

After having fixed the position of the displacement plate 40 as a wholethrough a rotational motion of the ring member 41 by a specified angle,fine positional adjustments of the tip of the arm member 42 will beperformed by means of piezo bimorphs. With the help of FIG. 14 and FIG.33, this operation will be explained hereunder.

By having the arm member 42 grounded and the voltages to be applied tothe electrodes 49 a, 49 b, 50 a and 50 b varied, the piezoelectriclayers 47 and 48 can be deformed freely for adjusting the position ofthe electrode 66 mounted on the tip of the arm member 42.

Suppose two different electric fields of opposing directions, forexample, are applied to the piezoelectric layers 47 and 48,respectively, the arm member 42 will be warped vertically since the twopiezoelectric layers situated on the upper and bottom surfaces of thearm member 42, respectively, have an expansion and contractionperformance different from each other and, in addition, the arm member42 is fixed at its one end only. Therefore, as illustrated in FIG. 33,the position of the electrode 66 at the tip of the arm member 42 can beadjusted very accurately along the direction vertical to the substrate44.

When electric fields of the same direction are applied to thepiezoelectric layers 47 and 48, respectively, the expansion andcontraction performance of the piezoelectric layers as a whole willbecome the same and the arm member 42 will be expanding or contractingin the longitudinal direction thereof. Therefore, the position of theelectrode 66 can be adjusted very accurately in either the arrow L orarrow N directions which are both in parallel with the substrate 44.

Further, on each of the piezoelectric layers 47 and 48 as shown in FIG.14, electric fields of opposing directions are applied to the right andleft sections, respectively. Then, since the expansion and contractionperformance differs between the right and left sections of the armmember 42, the arm member 42 will be showing a right and leftdeformation to make it possible to adjust finely the position of theelectrode 66 additionally in the directions of arrow V or arrow W, whichare both in parallel with the substrate 44.

Lastly, when the excitation is removed at the same time from theelectrodes 46 a through 46 i and the electrode 52, the ring member 41will be readily returned to the initial position as shown in FIG. 12 dueto the rebounding force of the elastically deformed beams 43 a through43 c.

The features of the microactuator so far explained in the aboveexemplary example of the present invention will be described hereunder.

First, the rotational motion of the ring member 41 is efficientlyconverted to and expanded in the almost linear motion of the tip of thearm member 42, leading to realization of a high accuracy positioningmechanism.

Besides, since the ring member 41 is in rolling contact with theelectrodes 46 a through 46 i and in rotation motion, the adverse effectsdue to friction are extremely small when compared with the first priorart example and the deterioration in performance caused by themechanical wear is minimized for a longer life.

Since good electrical conduction between the displacement plate 40 andthe shield layer on the substrate 44 is achieved securely through thebeams 43 a through 43 c, the displacement plate 40 and the shield layer44 are kept at the same potential at all times, resulting in highlyreliable motional characteristics.

When the displacement plate 40 starts to move, its position restrictingmember 56 and the guide member 57 of the electrode 46 a areelectrostatically coupled and closely brought into contact with eachother enabling the displacement plate 40 to return to its initialposition securely.

On account of each respective electrode having the same circular arcconfiguration, the ring member 41 can be rotated in a step-like motionby exciting the neighboring electrodes through application of the samevoltages and by shifting its position successively by the distance equalto one electrode spacing.

Further, by having the spacing pitch angles between two neighboringelectrodes changed properly, it becomes possible to shift the positionof the tip of the arm member 42 at an equal pitch, leading torealization of a higher accuracy positioning mechanism.

When the displacement plate 40 stops its motion, the arm member 42 canbe attracted electrostatically by exciting the electrode 52 on thesubstrate 44 for enabling the arm member 42 to keep its positionsecurely and enhancing the positioning reliability.

By having the arm member 42 of the displacement plate 40 constructed bypiezoelectric bimorphs, it is possible to adjust finely the position ofthe arm member 42 in the directions vertical to the substrate 44. As aresult, it is made possible to realize a positioning mechanism of asimple structure, yet having high accuracy.

When the displacement plate comes to an end of its motion, thedisplacement plate 40 can be readily returned to its initial positiondue to the rebounding force of the beams 43 a through 43 c simply uponremoving the excitation from the electrodes 46 a through 46 i and theelectrode 52.

Accordingly, the displacement plate 40 can be controlled with excellentreproducibility.

Furthermore, the high torque feature inherent to the wobble motion asdescribed in the prior art example can be utilized. Also, everycomponent element is laid out on a plane and the whole structure can befabricated by the semiconductor processes for a design of reduced sizeand weight and also for excellent mass-producibility.

Moreover, it is possible to design a structure wherein an arm member issupported by an axis by means of a free joint, electrodes each having acircular arc configuration are arranged opposing to the tip of the armmember, said electrodes are excited alternatingly and the arm member'srotational motion is controlled for a positioning purpose. However, withthis kind of structure, the speed reduction effect of the wobble drivingwill be lost, resulting in a problem of a reduced torque for driving thearm member.

Also, it is possible to think of a structure wherein the diameters ofthe ring member and the electrodes are made larger and inside thereofare arranged the arm member and its tip. When this structure isemployed, a higher torque will be obtained but compactness can notpossibly be achieved. The structure as described in the above exemplaryembodiment of the present invention, wherein displacement due to rollingrevolution is converted to almost linear displacement and also expanded,is more desirable for achieving compactness.

As explained in the foregoing, a first structure of the third exemplaryembodiment of the present invention comprises a displacement plate whichis provided with a ring member and an arm member put together, aplurality of electrodes arranged along the outer circumference of saidring member and a driving means whereby the position of the tip of saidarm member put together with said ring member can be adjusted by havingsaid ring member drawn to said electrodes alternatingly and rotated.

The foregoing structure has the operational effects as follows:

According to the present invention, a plurality of electrodes arrangedalong the circumference of a ring member of a displacement plate areapplied with voltages selectively, said ring member is alternatinglyattracted to said electrodes electrostatically and rotated to move thedisplacement plate as a whole. At this time, an arm member put togetherwith the ring member is also moved and its tip follows an almost lineartrace on account of its position situated outside said electrodes.Therefore, the rotational motion of the ring member is efficientlyconverted to an almost linear motion of the tip of the arm member,enabling said motion to realize a high accuracy positioning mechanism.

Also, a second structure of the third exemplary embodiment of thepresent invention comprises:

a displacement plate which is provided with a ring member and an armmember extending outwards from said ring member, both being puttogether;

a plurality of spiral beams located inside said ring member at positionssymmetric with respect to the center of said ring member, each of whichis connected at one end with an anchor formed solidly on a substrate andat the other end with a specified place of the inner circumference ofsaid ring member to support said displacement plate elastically;

a plurality of electrodes arranged along the outer circumference of thesubstrate except for the area occupied by said arm member of said ringmember; and

a voltage application means whereby voltages are applied selectively tosaid respective electrodes to have said ring member attractedelectrostatically and rotated for controlling the position of the tip ofsaid arm member.

The foregoing structure has the operational effects as follows:

According to the present invention, the ring member of the displacementplate is fixed onto the substrate by means of beams for securelyconnecting electrically with said substrate, resulting in realizing ahighly reliable notional performance. Also, on account of the rollingcontact existing between the electrodes and the ring member while thelatter is rotating, friction is made extremely small for achieving alonger life. Besides, the motion of the displacement plate causes thespiral beams to be deformed elastically and once the excitation imposedon the electrodes is removed the displacement plate will be readilyreturned to its initial position due to the rebounding force of thebeams. Therefore, a positioning mechanism with high accuracy andexcellent reproducibility can be realized. In addition, every componentelement can be laid out on a plane and semiconductor processes can beutilized in fabricating the actuator which excels in achieving a smallersize and light weight as well as mass-producibility.

Also, a third structure of the third exemplary embodiment of the presentinvention is the same as the second structure except for havingadditionally an electrode formed on the substrate at a place opposite toat least one portion of the arm member in order to have the position ofsaid arm member maintained.

The foregoing structure has the operational effects as follows:

The arm member is attracted electrostatically towards the substratethrough excitation of the electrodes, which are formed on the substrateand located at the position opposing to the arm member of thedisplacement plate, and held securely at that particular position forachieving highly reliable positioning.

Also, a fourth structure of the third exemplary embodiment of thepresent invention comprises:

a displacement plate provided with a ring member and an arm memberdeposited with piezo elements, both being put together;

a plurality of electrodes arranged along the outer circumference of saidring member;

a voltage application means whereby voltages are applied selectively tosaid respective electrodes to have said ring member attractedelectrostatically and rotated for controlling the position of the tip ofsaid arm member; and

a means to drive said piezo elements for fine adjustment in position ofthe tip of said arm member.

The foregoing structure has the operational effects as follows:

Positioning of the entire displacement plate including the arm membercan be first performed by electrostatic driving of the ring member andthen finer positioning of the tip of the arm member and furtherpositioning thereof in the directions vertical to the substrate can beperformed through deformation of the arm member caused by driving thepiezo elements which are deposited on the arm member. Thus, it becomespossible to realize a fine positioning mechanism of a simple structure.

EXAMPLE 4

The structure of a microactuator as a fourth exemplary embodiment of thepresent invention will be briefly explained with the help of drawings inthe following.

What differs from Example 3 is in having both the outer circumference ofthe ring member 41 and the inner circumference of the electrodes 46 athrough 46 i prepared so as to show undulating contours.

FIG. 34 is a plan view of said microactuator. Both the outercircumference of the ring member 41 and the inner circumference of theelectrodes 46 a through 46 i show sinusoidal wave-like contours of thesame wave length and amplitude against the respective reference circles.In addition, an insulating layer is formed on the inner circumference ofeach of the electrodes 46 a through 46 i in the same way as was inExample 3 but it is not shown in FIG. 34 because of the complexityinvolved with its expression.

Suppose the reference circles for the outer circumference of the ringmember 41 and for the inner circumference of the electrodes 46 a through46 i are 272 μm and 280 μm in diameter respectively, for example. Sincethere is a gap of 4 μm between the two reference circles, there will notbe any contacting points between the two kinds of circumference as longas the amplitude of the sinusoidal wave is 1.5 μm. Also, by splittingthe circumference of the two reference circles into 34 and 35 sectionsrespectively, sinusoidal wave forms having the same wave length (25.1μm) can be realized.

The fabrication processes of the microactuator of this exemplaryembodiment are the same as employed in Example 3 except for the process(1) as shown in FIG. 26, wherein the mask pattern to be used inpatterning by reactive ion etching (RIE) has to be changed.

Next, the operational performance of the microactuator as described inthe present exemplary embodiment will be explained with the help of FIG.35 and FIG. 36. FIG. 32 also has to be referred to.

First, upon application of the same voltage to the electrodes 46 a and46 b, the ring member 41 will be attracted electrostatically towardssaid electrodes and moved in the direction OA as indicated in FIG. 35until it comes into contact with the insulating layer (not shown in FIG.35) of the electrode surface. At this moment, the position restrictingmember 56 of the displacement plate 40 hits and stays in contact withthe guide member 57 of the electrode 46 a and also the outercircumference of the ring member 41 comes closely into contact with theelectrode 46 b, thus enabling the displacement plate 40 to be guided toa specified position for its initialization. Also, the electrode 66mounted on the tip of the arm member 42 is guided to the position 67 aas indicated in FIG. 31.

According to the same way as was in Example 3, as the pair of electrodesto be excited is shifted by one electrode length alternatingly, the ringmember 41 will be revolving in the direction of an arrow X by beingattracted by the excited two electrodes successively. When voltages arelastly applied to the electrodes 46 h and 46 i, the electrode 66 mountedon the tip of the arm member 42 will be guided to a position 67 h asindicated in FIG. 32.

As the ring member 41 is moved by rotating, the extent of deformation ofthe beams 43 a through 43 c will be increasing and the rebounding energyto push back the ring member 41 will be becoming greater. As a result,slipping will be likely to occur at the contacting place between thering member 41 and the electrodes 46 a through 46 i.

In the case of the microactuator of the present exemplary embodiment,the displacement plate 40 is moved while the undulated outercircumference of its ring member is engaged with the undulated innercircumference of the electrodes. Therefore, slipping does not occurbetween the contacting surfaces of the ring member 41 and the electrodes46 a through 46 i and the displacement plate 40 can be moved accuratelyand securely.

Also, the electrostatic force working as the prime motive force isproportional to surface areas. By employing an undulated contour as theinner circumference of the electrodes, the contacting surfaces will beincreasing, also resulting in securing the surest driving of thedisplacement plate 40.

Therefore, according to the present exemplary embodiment, the featureson top of the ones as described in Example 3 can contribute torealization of a microactuator of much higher reliability.

EXAMPLE 5

A fifth exemplary embodiment of the present invention, which correspondsto claims 16 and 17 will be explained hereunder.

FIG. 37 is a schematic plan view to show the structure of a multi-probehead for a scanning probe microscope as an exemplary embodiment of thepresent invention's microactuator and FIG. 38 is an expanded plan viewfor explaining how it is operated. The dimension of the whole structureis very small measuring 2 to 3 mm in outer diameter.

As shown in FIG. 37, a multi-probe head 110 is constructed in such a waythat six probes 112 through 117 are arranged along the circumference ofa silicon substrate 111. Each of the probes 112 through 117 is providedwith one of the driving circuits 118 through 123, which are created onthe silicon substrate 111 together with wirings and also the probes 112through 117 by the semiconductor processes.

Item 111 a is a cavity situated in the central portion of the siliconsubstrate 111, which is structured so as not to interfere with themotion of arms 124 through 129 of the probes 112 through 117,respectively. Also, probing needles 130 through 135 are mounted on thetip of the arms 124 through 129, respectively.

As shown in FIG. 37, the probes 112 through 117 are located at positionswhich are symmetric with respect to the center of the substrate 111 and,in addition, are able to rotate a little. In FIG. 37, the probe 115 onlyis shown to have rotated counter-clock wise by about 8 degrees. As aresult, the probing needle 134 at the tip of the arm 127 is located justat the center of the cavity 111. At this position, measurement of aspecimen (not shown in the drawings) can be conducted by means of theprobing needle 134. The other probing needles 130 through 133 and 135are situated on a circumference indicate by a one dot broken line and ina waiting mode of measurement.

As a matter of course, the same operation is applicable to any of allthe probes 112 through 117. For example, the probe 115 is rotated clockwise by about 8 degrees and the probe 113 is rotated this timecounter-clock wise by about 8 degrees to bring the probing needle 132 atthe tip of the arm 125 to the center for enabling the probing needle 132to perform measurement of a specimen.

By having the probe 113 prepared for measurement according to a systemdifferent from that of the probe 115 (the probe 113 for STM and theprobe 115 for AFM, for instance), the same place of a specimen can beobserved multi-purposely according to diversified methodology.

It has been so far indicated that the positions of the probes 112through 117 can be controlled with considerable freedom by the drivecircuits 118 through 123, though a detailed description will be given tothe rotating motion of the probes later. Besides, any positions can betaken by a probe as far as the positions fall on the path of itsrotating motion and six different probing needles 130 through 135 can bemoved to various places on a specimen at the same time.

In FIG. 38, how this is performed will be shown by an expandedillustration. The arms 124 through 129 fix individually the positions ofthe corresponding probing needles 130 through 135 and even if all theprobes 112 through 117 function according to the same measurementsystem, an extremely dynamic observation of an object can be realized.(In FIG. 38, the probes 114 and 115 are in the same state as were inFIG. 37 and the probe 114, e.g. the probing needle 133 at the tip of thearm 126 only is still in a waiting mode of measurement.)

Next, with the help of FIG. 39 through FIG. 41, a detailed descriptionof the structure of each of the probes 112 through 117 will be made.Since all the probes 112 through 117 have the same structure, anexplanation will be made on the probe 112 on behalf of all of the otherprobes. Also, as stated before, each respective probe is essentially ofthe same construction as the microactuator of the third exemplaryembodiment of the present invention and the explanation of the probeswill be made as simple as possible.

FIG. 39 is a schematic plan view to show the structure of the probe 112.

FIG. 40 is a longitudinal sectional view of said probe along the brokenline of POQ and looked in the direction T as shown in FIG. 39.

FIG. 41 is a traverse sectional view of said probe along the broken lineof RS and looked in the direction U as shown in FIG. 39.

As illustrated in FIG. 39 through FIG. 41, the probe 112 is formed of anelectroconducting thin plate-like material and comprised of a gaff-likearm 124 and a ring 136, both being put together. As mentioned before,the probe 112 is as a whole rotated and this is due to the rotationalmotion, which the ring 136 has been brought into electrostatically, andalso the arm 124 is piezoelectrically driven by piezo elements asexplained later.

There are three narrow beams 137 a through 137 c of an identical spiralconfiguration attached to the inner circumference of the ring 136 atthree different positions thereof separated from each other by 120degrees and located symmetrically from each other. One end of thesebeams is fixed to an anchor 138 which is mounted on the substrate 111and standing thereupon. In other words, the probe 112 is supported bythe anchor 138 elastically by means of the beams 137 a through 137 c.

On an area of the silicon substrate 111 extending beyond the outercircumference of the ring 136, nine electrodes 139 a through 139 i (onlythe electrode 139 e is shown in FIG. 40) are laid out along acircumference with a small gap left between the electrodes 139 a through139 i and the ring 136. The inner circumference of each respectiveelectrode except for the electrode 139 a is of one identical circulararc configuration. However, each respective electrode is not located atan equal spacing pitch angle from each other. Lines OB through OHexpress the reference lines, with respect to which the two neighboringelectrodes are symmetric and the spacing pitch angles ∠AOB, ∠BOC, ∠COD,∠DOE, ∠EOF, ∠FOG and ∠GOH are not the same. Also, the electrodes 139 athrough 139 i are connected by wiring with a voltage supply means (notindicated in FIG. 37) so that arbitrarily selected voltages can beapllied to the electrodes.

The probe 112 has a concave position restricting member 140 at the placeopposite to the electrode 139 a. The electrode 139 a, instead, has aconvex guide member 141 which comes together with the positionrestricting member 140 and directs the motion of the probe 112. Besides,there are insulating layers 142 a through 142 i formed on the innercircumference of each of the electrodes 139 a through 139 i to preventthe electrodes from making a direct electrical contact with the ring136.

Also, there is an electroconducting shield layer 143 of almost the sameshape as the ring 136 placed between the anchor 138 and the siliconsubstrate 111 so as to maintain an electrical connection with the ring136 at all times. Besides, an insulating layer 148 is formed over thesurface of the silicon substrate 111.

The arm 124 is sandwiched between thin film piezo elements 144 and 145.In addition, electrodes 146 a through 146 c are formed on the thin filmpiezo element 144 and electrodes 147 a and 147 b of almost the sameshape as the electrodes 146 a and 146 c are formed on the bottom of thethin film piezo element 145. Further, a cone shaped probing needle 131is created on the electrode 146 c.

Besides, the electrodes 146 a through 146 c and 147 a through 147 c canbe applied with arbitrarily selected voltages through wirings from avoltage supply means although it is not shown in the drawings.

Since the fabrication processes for said probe 112 are the same asemployed for the third exemplary embodiment of the present invention,the explanation thereof will be omitted.

Next, the operation of the probe 112 thus structured will be describedhereunder with the help of FIG. 42 through FIG. 44.

When the electrodes 139 a and 139 b are excited by application ofvoltages of the same magnitude, the ring 136 of the probe 112 will beattracted electrostatically by said two electrodes 139 a and 139 bsimultaneously and moved in the direction of OA as indicated in FIG. 42until it comes into contact with the insullating layers 142 a and 142 b.At this time, the position restricting member 140 of the probe 112 hitsand comes into contact with the guiding member 141 on the electrode 139a and also the periphery of the ring 136 comes into close contact withthe electrodes 139 a and 139 b. As a result, the probe 112 will beguided to a specified position for its initialization. Consequently, theprobing needle 131 mounted at the tip of the arm 124 will be guided to aposition 153 a as indicated in FIG. 42, e.g. a position (located on acircumference indicate by a one dot broken line) of a waiting mode formeasurement in FIG. 37 and FIG. 38.

Next, when the excitation of the electrode 139 a is removed and voltagesare applied to the electrodes 139 b and 139 c, the ring 136 will beattracted electrostatically by the two newly excited electrodes 139 band 139 c as shown in FIG. 43 and moved by rotating to a position whichis symmetric with respect to the line OB. Then, the probing needle 131will be guided to a position 153 b as indicated in FIG. 43, e.g. aposition (located inside a circle indicated by a one dot broken line) ofa ready mode for measurement in FIG. 37 and FIG. 38.

As the pair of electrodes to be excited is shifted by one electrodelength alternatingly, the ring 136 will be revolving in the direction ofan arrow J by being attracted by the excited two electrodessuccessively. However, as the ring 136 is moved while it is in rollingcontact with the electrodes 139 a through 139 i, it will be rotating bythe difference in length between its outer circumference and the innercircumference laid out by the electrodes 139 a through 139 i. Thedirection of its rotation will be in the direction of an arrow K or inthe direction opposite to its revolution.

This performance represents what is referred to as the wobble drivingsystem, which is characterized by realizing a torque of revolutionenlarged proportionately according to the ratio of speed reduction sincethe speed of revolution is greatly reduced in comparison with that ofrotation, achieving the same effect as speed reduction.

When voltages are lastly applied to the electrodes 139 h and 139 i, thering 136 will be moved to a position which is symmetric with respect tothe line OH as indicated in FIG. 44. Then, the probing needle 131 willbe guided to a position 153 h as indicated in FIG. 44, e.g. the centerposition (the center of a circle indicated by a one dot broken line)where the probing needle is ready for measurement. Thus, the rotationalmotion of the ring 136 is efficiently converted to an almost linearmotion of the tip of the arm 124.

On account of the identical circular arc configuration that eachrespective circumference of the electrodes 139 a through 139 i assumes,the ring 136 will be attracted electrostatically to the center of twoneighboring electrodes upon application of voltages of the samemagnitude to said two electrodes.

Therefore, by shifting the electrode pairs to be excited by oneelectrode length successively, it will be possible to give a step-likerotating motion to the ring 136.

Further, by having the rotational angle of the ring 136 varied mostsuitably through alteration of spacing pitch angles between twoneighboring electrodes, it will be made possible to have the tip of thearm 124 shifted at an equal pitch in a specified direction (thedirection L in FIG. 44, for example). Accordingly, it will be possibleto realize a high accuracy and highly dependable positioning mechanism,whereby the probing needle 131 can be guided at an equal pitch withrespect to the line L to the position 153 a (in a waiting mode formeasurement) through the position 153 h (the center position) asillustrated in FIG. 44.

The features associated with the foregoing structure are common to someextent with those as described in the third exemplary embodiment of thepresent invention and only a brief explanation will be given here.

On account of the wobble driving system as employed with said structure,the adverse effect due to friction has been made extremely small with aresultant contribution to reduced deterioration in performance andlonger life.

Also, the stabilized motion due to an appropriate application of holdingforce and the motion of recovering the initial position upon removal ofelectrical excitation can be achieved with said structure.

In addition, said structure has the advantage of gaining highly reliabledriving characteristics.

Besides, by having the arm 124 grounded and the voltages across theelectrodes 146 a, 146 b, 147 a and 147 b controlled, it will be possibleto deform the thin film piezo elements 144 and 145 with much freedom,enabling the probing needle 131 on the tip of the arm 124 to adjust itsposition finely. A detailed explanation of above will be omitted.

As explained in the foregoing, the structure of the fifth exemplaryembodiment of the present invention includes a multi-probe head, whereina plurality of probes, each having a probing needle on the tip thereof,are arranged along a circumference and each respective probe comprises:

a displacement plate put together with a ring member and an arm member,which extends outwards from said ring member, has piezo elementsdeposited on the both sides and has said probing needle on the tip;

a plurality of electrodes arranged on a substrate along the outercircumference of said ring member except for the place where said armmember is located;

a voltage application means whereby voltages are applied selectively tosaid electrodes to have said ring member attracted electrostatically bythe electrodes imposed with said voltages and moved by rotating; and

a means to drive said piezo elements so as to have a specimen scanned bysaid probing needles.

The foregoing structure has the operational effects as follows:

According to the present invention, an actuator as used as the probe isas a whole moved by rotating through selective application of voltagesto the electrodes arranged along the outer circumference of the ringmember. At this time, the probing needle on the tip of the arm memberwill be moved following an almost linear path. Accordingly, it will bemade possible for the probing needle to move easily on a specimen. Thismakes it also possible to have the plurality of probes arranged incircle exchanged efficiently or to have them moved on the specimen forscanning a plurality of places thereupon.

EXAMPLE 6

A sixth exemplary embodiment of the present invention will be explainedhereunder.

FIG. 45 is a perspective view of recording and reproducing equipmentwhich uses pickup heads composed of a microactuator as described in theexemplary embodiments of the present invention.

A 7.2 mm diameter disc composed of polysilicon with boron added iscontained inside a casing 201 of about 10 mm square and a terminal board203 only extends out of the casing. The total thickness of the casing isabout 2 mm. The whole structure looks like a hard disc unit but thereexists no concept of an assembly unit. On account of the dimension of 10mm square, it is inherently impossible for the concept of assembly,adjustment, or the like to get in.

When a charge injection recording of probing needle system as wasintroduced as the conventional technology is performed with theforegoing equipment, it will be possible to record about 800 M byte on adisc measuring 7.2 mm in diameter. The equipment is extremely simple inconstruction on account of a mere probing needle used as a head,enabling us to build such an extremely compact disc drive.

Now, the internal structure of said recording and reproducing equipmentis shown in FIG. 46.

There are an upper substrate 204 and a lower substrate 214, both formedof single silicon crystal, inside the casing 201. These two substratesare joined with each other with a terminal board 203 held between saidtwo substrates and covered by the casing 201 completely and sealed offfrom outside. Therefore, the inside of the casing 201 can be kept inarbitrary conditions, such as under reduced ambient pressure or invacuum or in nitrogen gas.

A disc 202 is held on the upper substrate 204 by means of a center bush205 so that it can rotate. a piezoelectric thin film 206 is formed onthe upper substrate 204 and when it is driven by ultrasonic waves, thedisc 202 can be rotated. An oxide layer and a nitride layer are formedon the surface 202 a of the disc 202 so that a charge injectionrecording of probing needle system can be performed. Control circuits207 and 208 are created on the upper substrate 204.

A plurality of a pickup head 210 is formed on the lower substrate 214opposite to the surface 202 a of the disc 202. The pickup head 210 is ofthe same structure as described in the third exemplary embodiment of thepresent invention and an explanation thereof will be reduced to aminimum as was in the fifth exemplary embodiment of the presentinvention.

Also, control circuits 209 and 209 a are created on the lower substrate214.

How the pickup heads using microactuators of the present exemplaryembodiment are arranged and also how the pickup heads make access to thedisc will be explained hereunder with the help of drawings.

FIG. 47 is a schematic plan view to show the positional relationshipbetween the disc 202 and each respective pickup head and FIG. 48 is apartially enlarged plan view to show the pickup head 240 c of FIG. 47and its vicinity.

As the recording method, a charge injection recording of probing needlesystem is to be employed here. According to this method, the recordingpit diameter measures 75 nm and a recording density per areacorresponding to 180 bit/μm² can be gained. When recording andreproducing are performed on one side of a 7.2 mm dia. disc, forinstance, the recording capacity will be as much as 800 M byte, providedthe recordable area extends from an inner diameter D1 (1.6 mm) to anouter diameter D2 (6.72 mm).

To begin with, the physical format on the disc 202 as used with thepresent exemplary embodiment will be briefly explained.

As shown in FIG. 47, the disc 202 is divided into 32 areas (referred toas cylinders hereafter) 250 a through 250 z and 251 a through 251 f,which are equally spaced in the radius direction, within the limits ofthe aforementioned recordable area. Incidentally, the width of eachrespective cylinder is 80 μm. Further, each cylinder is divided into 8areas (referred to as sectors hereafter), each measuring 10 μm in widthand being equally spaced from one another in the radius direction of thedisc 202.

As illustrated in FIG. 48, the cylinder 250 m, for instance, is dividedinto sectors 252 a through 252 h. Furthermore, each sector is dividedinto 132 tracks, which are again equally spaced in the same direction asabove (75 nm in width, not shown in FIG. 48).

Now, six blocks of pickup heads, each consisting of 240 a through 240 f,241 a through 241 f, 242 a through 242 e, 243 a through 243 e, 244 athrough 244 e, and 245 a through 245 e, respectively, are arranged onthe substrate along six different radii, which extend from the center ofthe disc 202 in six radial directions, at an equal pitch (480 μm)between one pickup head and another in the quantities of 5 or 6. All ofthese pickup heads have a probing needle 236 for recording andreproducing, and also created by integration on the lower substrate 214.In addition, the positions of the pickup heads of the neighboringblocks, 240 a through 240 f and 241 a through 241 f for example, areshifted by 80 μm in the distance away from the center of the disc 202between one another. In other words, the pickup heads 240 a, 241 a, 242a, 243 a, 244 a, 245 a, 240 b, 241 b . . . are located in this order by80 μm away from the center of the disc 202 in the radial directions and32 pickup heads all together are arranged in this way.

Therefore, by selecting any arbitrary pickup head electrically, it willbe possible to make an automatic access to each respective cylinder. Forexample, the pickup head 240 c is responsible for recording andreproducing in the cylinder 250 m. The explanation that followshereunder will be made in relative to said pickup head 240 c.

The access to the eight sectors 252 a through 252 h in the cylinder 250m is conducted by applying a wobble drive electrostatically to the ringmember 211 of the pickup head 240 c, as explained before. The positions237 a through 237 h in FIG. 48 show how the probing needle changes itsposition and the path thereof is almost the same as the line O′P′passing through the center O′ of the disc 202. Besides, each of saidpositions is located almost in the center of the sectors 252 a through252 h, respectively. At this time, the movement pitch of the probingneedle 236 is 10 um, which is the same as the width of the sector, andthe movement range is ±35 μm.

Also, access to 132 tracks within each sector is performed by applying aspecified voltage to each respective electrode of the arm member 212 ofthe pickup head 240 c and having the thin film piezo elements 217 and218 deformed freely to move the probing needle 236 slightly. At thistime, the movement pitch of the probing needle 236 is 75 nm, which isthe same as the width of the track, and the movement range is ±5 μm.

In addition, in case where the probing needle 236 is to be moved in thedirection perpendicular to the disc surface 202 a, the arm member 212 ofthe pickup head 240 c should be deformed piezoelectrically asillustrated in FIG. 49.

The foregoing is summarized as follows:

By selecting the pickup head 240 c electrically from a plurality ofpickup heads placed in order, access to the cylinder 250 m is firstperformed. Next, access of the probing needle 236 to the sector 252 a isachieved through a coarse electrostatic wobble movement of the ringmember 211 of the pickup head 240 c.

Further, access to each respective track is conducted by having the armmember 212 of the pickup head 240 c finely moved by means of thepiezoelectric bimorphs. Accordingly, each respective pickup head can putits probing needle 236 at an arbitrary position on the disc 202accurately for recording or reproducing upon application of biasvoltages.

Besides, use of the so called Zone-CAV system, whereby the angularvelocity is kept constant for each sector, as the method of rotating thedisc 202 makes it possible to achieve recording of higher density.

Thus, according to the present invention, all the component elementsfrom pickup head to disc can be fabricated by the semiconductorprocesses which excel in microminiaturization and mass-producibility,and also microactuators that are prepared in batches, not one by onethrough a conventional assembly work, can be provided for achievingremarkable micro-miniaturization and high performance with recording andreproducing equipment.

Also, according to the present invention, recording and reproducingequipment, whereby simultaneous recording and reproducing with extremelyhigh accessibility is achieved on account of arrangement of a pluralityof pickup heads, each mounted with a probing needle serving as a head,can be provided.

As explained in the foregoing, a first structure of the sixth exemplaryembodiment of the present invention comprises:

a disc-like rotational recording medium and a driving means thereof;

a pickup head composed of a ring member and an arm member, which haspiezo elements deposited thereupon and a probing needle mounted on thetip thereof;

fixed electrodes arranged along the outer circumference of said ringmember; and

a driving means to have said probing needle positioned on said disc-likerotational recording medium through coarse movement of said arm memberdue to the rotation of said ring member caused by the electrostaticattracting force working between said fixed electrodes and said ringmember upon application of voltages to said fixed electrodes and throughfine movement of said arm member due to its own deformation caused bysaid piezo elements.

The aforementioned structure has the operational effects as follows:

According to the present invention, a position of a probing needle canbe fixed on a disc-like rotational recording medium through rotationalmovement of a ring member and fine movement of an arm member. All themotions can be performed by voltage application to fixed electrodeswhich are arranged along the outer circumference of the ring member andalso by piezoelectric thin layers deposited in bimorph structure on thearm member. In addition, all the elements contributing to the abovemotions can be fabricated by semiconductor processes which excel inmicro-miniaturization and mass-producibility. Besides, there is a simpleprobing needle as a recording and reproducing means, which changes itsposition just by rotational or linear movement, not by act of sliding.Therefore, a microactuator serving as a pickup head which does notrequire any assembly work and adjustment can be provided by the presentinvention.

Also, a second structure of the sixth exemplary embodiment of thepresent invention comprises a first substrate having a disc-likerotational recording medium and a driving means thereof, and a secondsubstrate having pickup heads and fixed electrodes, both being puttogether so as to have the probing needles on said pickup heads faced tosaid rotational recording medium.

The above structure has the operational effects as follows:

According to the present invention, a first substrate and a secondsubstrate, both being already equipped with the required componentelements respectively, are put together for completion of equipment.Therefore, a microactuator of an entirely new fabrication method that isdifferent from the conventional concept of assembly work can be providedby the present invention.

As explained in the foregoing, the structures according to the presentinvention make it possible to produce long life and excellentreliability microactuators, whereby highly accurate positioning of goodrepeatability can be performed and the present invention's benefitreceived by the industry is extremely great.

In addition, by using the microactuators in a multi-probe head of ascanning probe microscope, a plurality of movable thin film probes canbe used simultaneously in observing various parts of a surface of aspecimen in a diversified manner.

Furthermore, by using the microactuators, which are produced accordingto an entirely new fabrication method derived of the concept differentfrom the conventional assembly work, as pickup heads of recording andreproducing equipment, it can be made possible to realizemicro-miniaturization and high performance that have not been thought ofbefore.

What is claimed is:
 1. A microactuator characterized by comprising: adisplacement plate which is provided with a ring member and an armmember put together; a plurality of electrodes arranged along the outercircumference of said ring member; and a driving means whereby theposition of the tip of said arm member put together with said ringmember can be adjusted by having said ring member attracted to saidelectrodes alternatingly and rotated.
 2. A microactuator characterizedby comprising: a displacement plate which is provided with a ring memberand an arm member extending outwards from said ring member, both beingput together; a plurality of spiral beams located inside said ringmember at positions symmetric with respect to the center of said ringmember, each of which is connected at one end with an anchor formedsolidly on a substrate and at the other end with a specified place ofthe inner circumference of said ring member to support said displacementplate elastically; a plurality of electrodes arranged along the outercircumference of the substrate except for the area occupied by said armmember of said ring member; and a voltage application means wherebyvoltages are applied selectively to said respective electrodes to havesaid ring member attracted electrostatically and rotated for controllingthe position of the tip of said arm member.
 3. A microactuator accordingto claim 2, wherein a plurality of electrodes, each having the samecircular arc configuration, are arranged with various pitch angles.
 4. Amicroactuator according to claim 2, wherein guide members to be coupledwith one another are formed on the displacment plate and on some of theelectrodes, respectively.
 5. A microactuator according to claim 2,wherein the outer circumference of the ring member of the displacementplate and the inner circumference of the electrodes are being preparedso as to show undulating contours, and the ring member moves by meshingwith the electrodes through these undulations.
 6. A microactuatoraccording to claim 2, wherein an electrode is formed on the substrate ata position opposite to at least a portion of the arm member in order tohave the position of said arm member maintained.
 7. A microactuatorcharacterized by comprising: a displacement plate provided with a ringmember and an arm member deposited with piezo elements, both being puttogether; a plurality of electrodes arranged along the outercircumference of said ring member; a voltage application means wherebyvoltages are applied selectively to said respective electrodes to havesaid ring member attracted electrostatically and rotated for controllingthe position of the tip of said arm member; and a means to drive saidpiezo elements for fine adjustment in position of the tip of said armmember.
 8. A multi-probe head, wherein a plurality of probes, eachhaving a probing needle on the tip thereof, are arranged along acircumference and each respective probe comprises: a displacement plateput together with a ring member and also with an arm member whichextends outwards from said ring member, has piezo elements deposited onthe both sides and has said probing needle on the tip; a plurality ofelectrodes arranged on a substrate along the outer circumference of saidring member except for the place where said arm member is located; avoltage application means whereby voltages are applied selectively tosaid electrodes to have said ring member attracted electrostatically bythe electrodes imposed with said voltages and moved by rotating; and ameans to drive said piezo elements so as to have a specimen scanned bysaid probing needle.
 9. A multi-probe head according to claim 8, whereineach respective probe has a plurality of spiral beams located insidesaid ring member at positions symmetric with respect to the center ofsaid ring member, each of which is connected at one end with an anchorformed solidly on the substrate and at the other end with a specifiedplace of the inner circumference of said ring member to support saiddisplacement plate elastically.
 10. Recording and/or reproducingequipment characterized by comprising: a disc-like rotational recordingmedium and a driving means thereof; a pickup head composed of a ringmember and an arm member, which has piezo elements deposited thereuponand a probing needle created on the tip thereof; fixed electrodesarranged along the outer circumference of said ring member; and adriving means to have said probing needle positioned on said disc-likerotational recording medium through general movement of said arm memberdue to the rotation of said ring member caused by the electrostaticattracting force working between said fixed electrodes and said ringmember upon application of voltages to said fixed electrodes and throughfine movement of said arm member due to its own deformation caused bysaid piezo elements.
 11. Recording and reproducing equipment accordingto claim 10, characterized by having a plurality of spiral beams locatedinside said ring member at positions symmetric with respect to thecenter of said ring member, each of which is connected at one end withan anchor formed solidly on a substrate and at the other end with aspecified place of the inner circumference of said ring member tosupport said displacment plate elastically.
 12. Recording andreproducing equipment according to claim 10, wherein the disc-likerotational recording medium comprises a dielectric substance formed anelectroconducting supportive body.
 13. Recording and reproducingequipment according to claim 10, wherein a plurality of pickup heads arearranged along the radial direction of the disc-like rotationalrecording medium at positions separated by an equal pitch.
 14. Recordingand reproducing equipment according to claim 10, wherein a firstsubstrate having a disc-like rotational recording medium and a drivingmeans thereof, and a second substrate having pickup heads and fixedelectrodes, both being put together so as to have the probing needles onsaid pickup heads faced to said rotational recording medium. 15.Recording and reproducing equipment according to claim 14, wherein thefirst substrate and the second substrate are hermetically sealed under areduced ambient pressure.